linux内核实验two实现过程#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <string.h>#include <sys/types.h>#include <sys/wait.h>#include <fcntl.h>#include <sys/stat.h>#include <dirent.h>#define normal 0 /*一般的命令*/#define out_redirect 1 /*输出重定向*/#define in_redirect 2 /*输入重定向*/#define have_pipe 3 /*命令中有管道*/int commandcounts=0;/*命令条数*/void print_prompt(); /*打印提示符*/void get_input(char *); /*得到输入的命令*/void explain_input(char *,int *,char a[100][256]); /*对输入命令进行解析*/void do_cmd(int ,char a[100][256]); /*执行命令*/int find_command(char *); /*查找命令中的可执行程序*/int main(int argc,char **argv){ int i; int argcount = 0; char arglist[100][256]; char **arg = NULL; char *buf = NULL; buf = (char *)malloc(256); if (buf == NULL){ perror("malloc failed"); exit(-1); } char* commands[10]; while(1){ /*将buf所指向的空间清零*/ memset(buf,0,256); print_prompt(); get_input(buf); /*若输入的命令为exit或logout则退出本程序*/ if (strcmp(buf,"exit\n") == 0 || strcmp(buf,"logout\n") == 0) break; //找出有几条命令，多条命令以分号分割 int index=0; commandcounts=1; for(index=0;index<strlen(buf);index++){ if(buf[index]==';') commandcounts++; } if(commandcounts>10){ printf("%s\n","commandcounts over.max num is 10"); continue; } index=0; char *p=strtok(buf,";"); do{ commands[index]=p; index++; } while(p=strtok(NULL,";")); for(index=0;index<commandcounts;index++){ for (i=0;i<100;i++){ arglist[i][0] = '\0'; } argcount = 0; explain_input(commands[index],&argcount,arglist); do_cmd(argcount,arglist); } } if (buf != NULL){ free(buf); buf = NULL; } exit(0);}void print_prompt(){ printf("myshell$$");}/*获取用户输入*/void get_input(char *buf){ int len = 0; int ch; ch = getchar(); while (len <256 && ch != '\n'){ buf[len++] = ch; ch = getchar(); } if (len ==256){ printf("commond is too long \n"); exit(-1); /*输入的命令过长则退出程序*/ } buf[len] = '\n'; len++; buf[len] = '\0';}/*解析buf中的命令，将结果存入arglist中，命令以回车符号\n结束*//*如输入命令为“ls -l /tmp”，则arglist［0］，arglist［1］，arglist［2］分别为ls,-l和/tmp*/void explain_input(char *buf,int *argcount,char arglist[100][256]){ char *p = buf; char *q = buf; int number = 0; while(1){ if (p[0] == '\n') break; if (p[0] == ' ') p++; else { q = p; number = 0; while ((q[0] != ' ') && (q[0] != '\n')){ number++; q++; } strncpy(arglist[*argcount],p,number+1); arglist[*argcount][number] = '\0'; *argcount = *argcount + 1; p = q; } }}void do_cmd (int argcount,char arglist[100][256]){ int flag = 0; int how = 0; /*用于指示命令中是否含有>,<,|*/ int background = 0; /*标识命令中是否有后台运行标识符*/ int status; int i; int fd; char *arg[argcount+1]; char *argnext[argcount+1]; char *file; pid_t pid; /*将命令取出*/ for (i=0;i<argcount;i++){ arg[i] = (char *)arglist[i]; } arg[argcount] = NULL; /*查看命令行是否有后台运行符*/ for (i=0;i<argcount;i++){ if (strncmp(arg[i],"&",1) == 0){ if (i == argcount - 1){ background = 1; arg[argcount-1] = NULL; break; } else { printf("wrong command\n"); return; } } } for (i=0;arg[i] != NULL;i++){ if (strcmp(arg[i],">") == 0){ flag++; how = out_redirect; if (arg[i+1] == NULL) flag++; } if (strcmp(arg[i],"<") == 0){ flag++; how = in_redirect; if (i == 0) flag++; } if (strcmp(arg[i],"|") == 0){ flag++; how = have_pipe; if (arg[i+1] == NULL) flag++; if (i == 0) flag++; } } /*flag大于1，说明命令中含有多个>,<,|符号，本程序是不支持这样的命令的， 或者命令格式不对，如“ls -l /tmp >”*/ if (flag > 1){ printf("wrong command\n"); return; } if (how == out_redirect){/*命令只含有一个输出重定向符号>*/ for (i=0;arg[i] != NULL;i++){ if (strcmp(arg[i],">") == 0){ file = arg[i+1]; arg[i] = NULL; } } } if (how == in_redirect){/*命令只含有一个输入重定向符号<*/ for (i=0;arg[i] != NULL;i++){ if (strcmp(arg[i],"<") == 0){ file = arg[i+1]; arg[i] = NULL; } } } if (how == have_pipe){/*命令只含有一个管道符号|*/ /*把管道符号后面的部分存入argnext中，管道后面的部分是一个可执行的Shell命令*/ for (i=0;arg[i] != NULL;i++){ if (strcmp(arg[i],"|") == 0){ arg[i] = NULL; int j; for (j=i+1;arg[j] != NULL;j++){ argnext[j-i-1] =arg[j]; } argnext[j-i-1] = arg[j]; break; } } } if ((pid = fork()) < 0) { printf("fork error\n"); return; } switch(how) { case 0: /*pid为0说明是子进程，在子进程中执行输入的命令*/ /*输入的命令中不含>,<和|*/ if (pid == 0){ if (!(find_command(arg[0]))){ printf("%s:command not found\n",arg[0]); exit(0); } execvp(arg[0],arg); exit(0); } break; case 1: if (pid == 0){ if (!(find_command(arg[0]))){ printf("%s: commandnot found\n",arg[0]); exit(0); } fd = open(file,O_RDWR|O_CREAT|O_TRUNC,0644); dup2(fd,1); execvp(arg[0],arg); exit(0); } break; case 2: /*输入的命令中含有重定向符<*/ if (pid == 0){ if (!(find_command(arg[0]))){ printf("%s:command not found\n",arg[0]); exit(0); } fd = open(file,O_RDONLY); dup2(fd,0); execvp(arg[0],arg); exit(0); } break; case 3: /*输入的命令中含有管道*/ if (pid == 0){ int pid2; int status2; int fd2; if ((pid2 = fork()) < 0){ printf("fork2 error\n"); return; } else if (pid2 == 0){ if (!(find_command(arg[0]))){ printf("%s:command not found\n",arg[0]); exit(0); } fd2 = open("/tmp/youdonotknowfile",O_WRONLY|O_CREAT|O_TRUNC,0644); dup2(fd2,1); execvp(arg[0],arg); exit(0);//子进程在此退出 } //父进程在此执行 if (waitpid(pid2,&status2,0) == -1) printf("wait for child process error\n"); if (!(find_command(argnext[0]))){ printf("%s:command not found\n",argnext[0]); exit(0); } fd2 = open("/tmp/youdonotknowfile",O_RDONLY); dup2(fd2,0); execvp(argnext[0],argnext); if (remove("/tmp/youdonotknowfile")) printf("remove error\n"); exit(0); } break; default: break; } /*若命令中有&,表示后台执行，父进程直接返回，不等待子进程结束*/ if (background == 1){ printf("[process id %d]\n",pid); return; } /*父进程等待子进程结束*/ if (waitpid(pid,&status,0) == -1) printf("wait for child process error\n");}/* * 产看这个命令是否存在 */int find_command(char *command){ DIR *dp; struct dirent *dirp; char *path[] = {"./","/bin","/usr/bin",NULL}; /*使当前目录下的程序可以运行，如命令"./fork"可以被正确解释和执行*/ if (strncmp(command,"./",2) == 0) command = command + 2; /*分别在当前目录、/bin和/usr/bin目录查找要执行的程序*/ int i = 0; while (path[i] != NULL){ if ((dp = opendir(path[i])) == NULL) printf("can not open /bin \n"); while((dirp = readdir(dp))!= NULL){//读目录中的所有的文件 if (strcmp(dirp->d_name,command) == 0){//有这个文件 closedir(dp); return 1; } } closedir(dp); i++; } return 0;}
